Control boxes are employed typically in the automotive area in order to transform a control signal into a mechanical movement and convey it to a part that needs to be controlled.
As an example, such control boxes are used for turbochargers, where they open and close a valve plate of an exhaust gas bypass in accordance with the requirements pertaining to a particular driving situation.
In this area of use, the requirements have been modified according to particular characteristics over time, in line with progress in automobile technology.
This evolution may be described approximately as follows:
A positive pressure—control box comprises, as shown in FIG. 1, an upper chamber 4 and a lower chamber 6 which are separated from each other by a membrane 12 in gas-tight manner. The upper chamber 4 includes a control duct 10 through which the upper chamber may either be set at atmospheric pressure (At) or at positive pressure up to a maximum pressure (Pmax). The pressure set at any moment may therefore vary between At and Pmax.
The lower chamber 6, which is open at 8, is continuously held at atmospheric pressure At. A helical spring 3 is arranged in the lower chamber 6 in a manner so as to solicit the membrane upwards.
The membrane 12 is connected to a rod 14 in a manner so as to be axially pulled or pushed by the membrane during its movement in the direction of movement (upwards or downwards) of the membrane.
If atmospheric pressure prevails in the upper chamber, the same pressure prevails on both sides of the membrane, and spring 3 pushes the membrane upwards and rod 14 is pulled upwards as well.
As illustrated schematically, this movement of rod 14 produces a lowering of valve plate 18 onto valve seat 19, thus closing the valve.
The force of spring 3 is chosen to be relatively high, because for the use of such a positive pressure control box for the closing of the by-pass valve a relative high force is needed, because the by-pass is subject to relatively high pressure, built up be the exhaust gases expelled from a combustion engine.
This type of pressure box has the disadvantage that it uses positive pressure, whereby the positive pressure has to be produced on demand, which creates a time lag.
Therefore, in the automobile technology one has shifted more to negative pressure—control boxes, since negative pressure is available from other components in the engine space of the vehicle.
A typical traditional negative pressure box is illustrated in FIG. 2.
The negative pressure—box in FIG. 2 includes also an upper chamber 4a and a lower chamber 6a which are separated from each other by a membrane 12a in gas tight manner.
A control duct 10a is susceptible to be connected to a non-illustrated negative pressure source. The lower chamber is open and is continuously held at atmospheric pressure.
In this control box, the spring is positioned in the upper chamber, so that, if atmospheric pressure prevails on both sides of the membrane 12a, spring 3a, membrane 12a and rod 14a are pushed downwards, so as to open valve 18, 19.
If the upper chamber is set to negative pressure, the atmospheric pressure in the lower chamber pushes the membrane upwards against the force of the spring and closes valve 18, 19. The force which is required to close the valve, is produced by the negative pressure in the upper chamber from which one needs to deduct the force of the spring.
This means, that for relative high closing forces, the surface of the membrane needs to be relatively large in order to translate the relatively small pressure difference between the strongest negative pressure and atmospheric pressure into a sufficiently high force.
A large membrane surface, however, requires an increase of the dimensions of the control box, which is disadvantageous for obvious reasons.
In order to overcome this disadvantage, the present inventors have invented another system, termed herein a bi-pressure control box.
FIG. 3 illustrates the principle of a bi-pressure control box. Upper chamber 4b and lower chamber 6b are again separated by a membrane 12b in gas tight manner. The upper chamber 4b includes a control duct 10b for the setting of a negative pressure in the upper chamber and the lower chamber has a control duct 20 for the setting of a positive pressure in the lower chamber.
Lower chamber 6b is closed by a sealing 22 which permits axial movement of rod 14b. Primarily, this control box acts in the same way as the control box of FIG. 2, but provides the further possibility to increase the closing force of the rod 14b by applying a positive pressure to the lower chamber 6b, because the force of the rod is the product of the membrane surface and of the pressure difference of at maximum Pmax—V (V=vacuum), minus the force of the spring. Due to the additional positive pressure-connection of the control box of FIG. 3, as compared to the control box of FIG. 2, the pressure component of the pressure difference between the chambers is increased.
The bi-pressure control box of FIG. 3 combines the advantage of the control box of FIG. 1 (high closing force due to strong spring) with the advantage of the control box of FIG. 2 (use of negative pressure) but loses a portion of this advantage, however, through the use of additional positive pressure.
It is therefore the object of the present invention to devise a control box which combines all partial advantages of the different states of the art, without increasing the size, while working with negative pressure only and whereby nevertheless a high closing force is obtained.
This object is achieved by a control box according to the claims herein.